1

17. Data Access

ADO.Net ArchitectureNew Features of ADO.NETVisual Studio Visual Studio Wizards and

Designers Demonstration: Creating Data ComponentsLab 17: Accessing Data Using ADO.NET

Code Samples

2

ADO.NET Architecture

What Is ADO.NET?What Is a Connected Environment?What Is a Disconnected Environment?What Is the ADO.NET Object Model?What Is the DataSet Class?What Is the .NET Data Provider?

3

What Is ADO.NET?ADO.NET is a data access technology. It provides: A set of classes, interfaces, structures, and

enumerations that manage data access from within the .NET Framework

An evolutionary, more flexible successor to ADO A system designed for disconnected environments A programming model with advanced XML support

4

What Is a Connected Environment?

A connected environment is one in which users are constantly connected to a data source

Advantages: Environment is easier to secure Concurrency is more easily controlled Data is more likely to be current than in other scenarios

Disadvantages: Must have a constant network connection Scalability

5

What Is a Disconnected Environment? In a disconnected environment, a subset of data from

a central data store can be copied and modified independently, and the changes merged back into the central data store

Advantages You can work at any time that is convenient for you, and can

connect to a data source at any time to process requests Other users can use the connection A disconnected environment improves the scalability and

performance of applications Disadvantages

Data is not always up to date Change conflicts can occur and must be resolved

6

What Is the ADO.NET Object Model?DataSetDataSet

DatabaseDatabaseDatabaseDatabase

.NET Data Provider.NET Data Provider

ConnectionConnection

TransactionTransaction

CommandCommand

ParametersParameters

DataReaderDataReader

DataAdapterDataAdapter

SelectCommandSelectCommand

InsertCommandInsertCommand

UpdateCommandUpdateCommand

DeleteCommandDeleteCommand

DataTableCollectionDataTableCollection

DataTableDataTable

DataRowCollectionDataRowCollection

DataColumnCollectionDataColumnCollection

ConstraintCollectionConstraintCollection

DataRelationCollectionDataRelationCollection

XMLXMLXMLXML

7

What Is the .NET Data Provider?

Manages the connection to a database

Manages the connection to a database

Executes a query command on the database

Executes a query command on the database

Exchanges data between the data set and the database

Exchanges data between the data set and the database

Provides efficient access to astream of read-only data

Provides efficient access to astream of read-only data

DatabaseDatabaseDatabaseDatabase

ConnectionConnection

CommandCommand

DataReaderDataReader

DataAdapterDataAdapter

8

Creating an Application That Uses ADO.NET to Access DataHow to Specify the Database ConnectionHow to Specify the Database CommandHow to Create the DataAdapter ObjectHow to Create a DataSet ObjectHow to Bind a DataSet to a DataGridHow to Use the Data Wizards in Visual Studio .NET

9

How to Specify the Database Connection Use the Connection object to:

Choose the connection type Specify the data source Open the connection to the data source

Use the connection string to specify all of the options for your connection to the database, including the account name, database server, and database name

string connectionStr = @"Data Source=localhost; Integrated Security=SSPI; Initial Catalog=northwind";

string connectionStr = @"Data Source=localhost; Integrated Security=SSPI; Initial Catalog=northwind";

10

How to Specify the Database Command

Create a string containing SQL statements Remember that Verbatim strings can make this much

easier!

Examples of SQL statements: SELECT * FROM Customers

SELECT CustomerName FROM Customers

SELECT * FROM Customers WHERE Country = 'Mexico'

string commandStr=@"SELECT CustomerName, CompanyName FROM Customers";

string commandStr=@"SELECT CustomerName, CompanyName FROM Customers";

11

How to Create the DataAdapter Object

Data sourceDataAdapterDataTable

DataTable

DataSet

DataAdapter

FillFill

UpdateUpdate

UpdateUpdate

FillFill

12

What Is the DataSet Class?

DataSetDataSet

ConstraintsConstraints

TableTable

ColumnColumn

ConstraintConstraint

RowsRows

RowRow

RelationsRelations

RelationRelation

ObjectObject CollectionCollection

TablesTables

ColumnsColumns

DataSets consist of one or more tables and relationsLoaded from one or more

data adaptersCreated as you workLoaded from XMLLoaded from other

DataSetsTables contain columns,

constraints, and rowsAll are collections!

13

How to Bind a DataSet to a DataGrid

DataGrid dataGrid1 = new DataGrid();sqlDataAdapter1.Fill(dataSet1, "Customers");sqlDataAdapter2.Fill(dataSet1, "Orders");dataGrid1.DataSource = dataSet1;

DataGrid dataGrid1 = new DataGrid();sqlDataAdapter1.Fill(dataSet1, "Customers");sqlDataAdapter2.Fill(dataSet1, "Orders");dataGrid1.DataSource = dataSet1;

To bind programmatically

14

Changing Database Records

How to Access Data in a DataSet ObjectHow to Update a Database in ADO.NETHow to Create a Database RecordHow to Update a Database RecordHow to Delete a Database Record

15

DataRowobjects

How to Access Data in a DataSet Object

DataColumnobjects

DataTableobjects

DataColumnobjects

16

How to Update a Database in ADO.NET

DataSet

Client

DataAdapter

DatabaseDatabaseDatabaseDatabase

Server

DataData

FillFill

UpdateUpdate

DeleteCommandDeleteCommand

UpdateCommandUpdateCommand

InsertCommandInsertCommand

DataData

DataTable

17

How to (Manually) Create a Database Record

Create a new row that matches the table schema

Add the new row to the dataset

Update the database

Create a new row that matches the table schema

Add the new row to the dataset

Update the database

DataRow myRow = dataTable.NewRow();DataRow myRow = dataTable.NewRow();

sqlDataAdapter1.Update( dataSet );sqlDataAdapter1.Update( dataSet );

dataTable.Rows.Add( myRow );dataTable.Rows.Add( myRow );

18

How to (Manually) Delete a Database Record

Delete the row from the dataset

Update the database

Accept the changes to the dataset

dataTable.Rows[0].Delete();dataTable.Rows[0].Delete();

dataSet.AcceptChanges();dataSet.AcceptChanges();

dataAdapter.Update(dataSet);dataAdapter.Update(dataSet);

19

Data Reader

Data Readers manage the stream of results from a SELECT statement or Stored Procedure

Data Readers are read only Data Readers only move forwards through the data –

they cannot go backwards No other database operation can be performed while

a data reader is open

20

Using a DataReader with a SELECT Statement

string queryString = "SELECT FirstName, LastName FROM dbo.Employees";

//Create the command objects SqlCommand com = new SqlCommand(queryString, conn);

//Call the command's ExecuteReader method SqlDataReader dr = com.ExecuteReader();

//Loop through the datareader to output the employee names while (dr.Read()) { listBox1.Items.Add(dr.GetString(0) + " " +

dr.GetString(1)); }

21

Using a DataReader to call a Stored Procedure

//Create the command object and set its properties SqlCommand com = new SqlCommand(); com.Connection = conn; com.CommandText = "CustOrderHist"; com.CommandType = CommandType.StoredProcedure;

//Create the parameter object and add it to the command's collection SqlParameter param =

new SqlParameter("@CustomerID", SqlDbType.NVarChar, 5); param.Value = txtID.Text; com.Parameters.Add(param);

22

Creating a Two Tier ApplicationCreate the data tier

Create a new class library projectCreate a class to represent a business entity, say

customersAdd methods that access the database, using ADO.NetAdd properties that expose attributes, say name, phone …

Create the presentation tierCreate a new Windows Application projectAdd a reference to the above data projectCreate an object from classUse the object’s properties to populate controls on a formUse the object’s methods to access the database

23

New Features of ADO.NET 2.0

Multiple active result setsOne connection can host more than one result setReduces number of connections on a database

Asynchronous operationsBegin a data access operation, continue with other tasks,

and then later end the original operation

Batch updatesUpdate multiple rows in one batchUse the UpdateBatchSize property of the DataAdapter

24

Visual Studio Wizards and Designers

Data Source Configuration WizardTableAdapter Configuration WizardTableAdapter Query Configuration WizardPreview Data Dialog Box

25

Lab 17: Accessing Data Using ADO.NET

Exercise 1: Retrieving Data into a Data Set Exercise 2: Updating the Database from a Data Set Exercise 3: Retrieving Data with a Data Reader Exercise 4: Calling a Stored Procedure